Photographic processing or developing is generally performed through chemical means by which a photographic film or a paper is treated after photographic exposure to produce a negative or positive image. Photographic processing transforms the latent image into a visible image or photo in a stable form, which is insensitive to light. Both black-and-white and color photos can be developed by chemical methods. For example, a negative can be obtained through photographic exposure on a photographic film such as a silver halide film and subsequent chemical treatment. A photo can be further developed or printed onto a photographic paper in a dark room.
In most darkrooms, an enlarger, an optical projector, and a control of light are used. A negative is placed in the enlarger. An image from the negative is enlarged and projected onto a photographic paper. The control is used to focus the enlarged image on the photographic paper, and adjust the intensity and duration of light exposure. The exposed paper is further developed through wet processes using developer and fixing agents.
When developing black-and-white prints, a safelight is commonly used to illuminate the work area. The majority of black-and-white papers are sensitive to only blue, or to blue and green light, so a red- or amber-colored light can be safely used without exposing the paper. However, color photographic papers, being sensitive to all parts of the visible spectrum, must be kept in complete darkness until the prints are properly fixed.